The present invention relates to wireless transceivers, and in particular to a wireless transceiver for use with existing cellular and PCS telephonic systems for communicating both AMPS and CDMA data.
In present day wireless telecommunications systems as shown in FIG. 1, a first wireless transceiver 120, such as a cellular telephone, communicates with a second wireless transceiver 150 via one or more "cells" 130. Each cell is employed to cover a geographical area, although some overlap may occur. Inter-cell communication is possible using handoff signals 136 communicated between cell sites.
Within each cell site 130, a base station 140 includes a receiver 142 and a transmitter 144. The receiver 142 receive signals either from users within the cell area or from an adjacent cell. The base station ascertains the destination of the received signals 132 and re-transmits them 134 via the transmitter 144 either within the cell area if the intended recipient is within the cell area or to another cell site closer to the intended recipient.
Each wireless transceiver 120 and 150 includes a transmitter 124 for transmitting signals 132 to the base station 140 and a receiver 124 for receiving the signals 134 transmitted from the base station 140. At present, two frequency bands are used for the received and transmitted signals. Base stations in the Cellular (cell) systems receive signals 132 in the frequency range of 824.04 MHz-848.97 MHz and transmit signals 134 in the frequency range of 869.04 MHz-893.97 MHz. PCS-band base stations receive signals 132 in the frequency range of 1851.25 MHz-1908.75 MHZ and transmit signals 134 in the frequency range of 1931.25 MHz-1988.75 MHz.
In addition to the two frequency bands available, two data modulation/demodulation techniques are also used to encrypt the data for transmission and to decipher the data when received by the intended user. The Advanced Mobile Phone System (AMPS), employs the techniques of Frequency Division Multiple Access (FDMA) to partition and reuse the available RF spectral bandwidth so as to increase the number of available users. In the AMPS implementation, a carrier consisting of a fraction of the total available bandwidth, typically 30 KHz, carries each channel's communications.
Direct Sequence (DS) Code Division Multiple Access (CDMA) is the newest data communication mode used in wireless telecommunications. In DS-CDMA systems, a unique coded address is assigned to each user. Data is transmitted to an intended recipient by superimposing the data onto an address waveform corresponding to the uniquely coded address of the intended recipient. The data has a relatively narrow bandwidth (typically 30 KHz) compared to the bandwidth of the address waveform (typically 1.23 MHz), resulting in the data being spread over the spectrum of the address waveform. The combined data+address waveform is then modulated onto a particular carrier frequency and transmitted. Although all users have access to the entire frequency band, only the intended recipient is able to decipher the transmission since he alone has the unique coded address needed to decode the data from the transmitted signal.
The transceivers 120 and 150 utilize a number of frequency synthesizers to generate the transmitting signals 132 and to downconvert the received signals 134 to extract the sent information. However, frequency synthesizers are expensive and dissipate large amounts of power, which reduces the transceiver's battery life. What is needed is a transceiver architecture and frequency plan which employs a minimum number of frequency synthesizers. Additionally, an improved transceiver architecture is needed which uses a minimum number of frequency synthesizers and which can handle both AMPS and CDMA-encoded signals.